why data rate below 500 bytes per secend

[wen]

i send 20 bytes per 10ms,but only receive 300 bytes per second from android,why?

[Alex]

Check connection interval. Some more information can be found here

[Ole Bauck]

The central (Android) probably does not accept the connection interval and sets its own as the link Alex posted says. Different Android phones support different connection intervalls, see here. Which SoftDevice are you using and are you sending the packets as notification?